1. Field of the Invention
The present invention relates to an image forming apparatus in which a latent image can be developed with the toner and transferred to a transfer sheet and wherein the transfer sheet having the transferred image thereon can properly be charge-removed or discharged under the action of charge removing means.
2. Description of the Prior Art
The prior art will be described in connection with an electrophotographic type color copying machine in which a toner image formed on a photosensitive image bearing member can be multi-transferred to the same transfer material or sheet by winding the transfer sheet around a transfer drum (transfer-sheet carrying member) arranged opposed to the photosensitive image bearing member and constituted of a dielectric mesh screen and by rotating the above transfer drum through predetermined number of revolutions. The transfer sheet is held around and is in intimate contact with the outer periphery of the transfer drum under the electrostatic attraction between the screen of the transfer drum, in addition to the leading edge of the transfer sheet being grasped by gripper means mounted on the transfer drum. After completion of the desired number of transfer steps, the transfer sheet will have to be separated from the transfer drum. However, the transfer sheet is charge-removed by means of a charge-removing device to relieve the electrostatic attraction when the leading edge of the transfer sheet is released from the grasp of the gripper. Such a charge removing step may be carried out upon each completion of the transfer steps for the purpose that the efficiency of transfer is prevented from decreasing during the multi-transfer process.
The charge removing function may undesirably decrease the electrostatic attraction of the transferred and non-fixed toner image on the transfer sheet so that the particles of the non-fixed toner will be scattered or that the transfer sheet will be deviated from a predetermined position on the transfer drum to reduce the resulting image in quality.
In the prior art electrophotographic type monochromatic copying machines, a toner image formed on a photosensitive drum is transferred to a transfer sheet fed in contact with the photosensitive drum, under the action of a transfer corona discharger at the transfer station. The transfer sheet is then separated from the photosensitive drum by subjecting the transfer sheet to the action of charge removing means to neutralize the electrostatic attraction between the photosensitive drum and the transfer sheet. Similarly, the charge removing action must suitably be controlled to avoid the above mentioned disadvantages.
It is, however, difficult to suitably control the charge removing action due to the influence of humidity in the prior art image forming systems including electrophotographic type copying machines.
The situation is the same as with image forming devices other than electrophotographic devices, if the similar charge removal after the image transfer is needed.